This keyword requests a general Complete Basis Set extrapolation of the MP2 energy [Nyden81, Petersson88, Petersson91, Petersson91a]. The method requires two parameters: the minimum number of pair natural orbitals and the integration grid. The first can be specified with the NMin option, and it defaults to 5 for the 6-31G**, 6-31G‡ and 6-311G** basis sets (with or without diffuse functions), and to 10 for the 6-311G basis set with (2df,p) or (3df,p) polarization functions (again, with or without diffuse functions). NMin must be specified in all other cases, or an error will result.
The default integration grid is the (99,590) grid; an alternate grid can be specified with the Int=Grid keyword. The integration portion is a small part of the total CBS extrapolation computation, so this relatively large grid was chosen. See the description of the Integral keyword for a full discussion of the available grids.
NMin=N
Specifies N as the minimum number of pair natural orbitals.
MinPopLocal
Use localization based on populations in minimal basis [Montgomery00]. This is the default.
PopLocal
Use population localization as described in reference [Pipek89].
BoysLocal
Use Boys localization [Boys60, Foster60, Boys66].
NoLocal
Do not use any localization.
NRPopLocal
Newton-Raphson population localization.
NRBoysLocal
Newton-Raphson Boys localization.
NRMinPopLocal
Use 2nd order minimal population analysis.
SaveOrbitals
Save the localized CBS orbitals to the read-write file. Note that they will replace the SCF orbitals.
Single point energy calculations only, using any electron correlation method.
Int=Grid, CBS keywords
Last update: 23 April 2013